1. Field of the Disclosure
The disclosure relates in general to a method for forming voids and a structure with voids formed using the same, and more particularly to a method for forming voids capable of resolving tombstone effect for components and a structure thereof.
2. Description of the Related Art
Along with the miniaturization and sophistication of electric products, such as photoelectric, communication and semiconductor products, the components used in laptops or mobile devices are getting slimmer and lighter. However, the surface mount technology (SMT) used for disposing components will result in more and more defects as the number of small components increases.
In the design of printed circuit board, if the pad located at one end of an element contacts a large copper foil while the pad located at the other end does not contact a large copper foil, the temperature of the pads at two ends of the element will be different during the reflowing process. FIG. 1A˜FIG. 1D are schematic diagrams of an element tombstone effect. As indicated in FIG. 1A, the solders 12a and 12b on the pads located at two ends of the element 11 are not melted and deformed. During reflow, the solders 12a and 12b approach reflow temperature, and the solders 12a and 12b begin to wet unevenly. The pads 12 are heated at different temperatures, the solder 12a at a higher temperature will be melted faster than the solder 12b at a lower temperature. Also, surface tension and torque increase on one side of the solder (such as the solder 12a). As indicated in FIG. 1B, the element 11 tilts at one end and causes the melted solder 12a′ to tumble down. As indicated in FIG. 1C, during the melting process, the solder 12a′, being affected by unstable temperature in the finance and track vibration, will flow towards the solder 12b′ located at the right hand side, and the surface tension will make the element 11 rotated and standing on end during reflow as indicated in FIG. 1D. Such phenomenon is called a ‘tombstone effect’. The lighter the element, the easier to pull the element upward and make the element stand on end during reflow.